300        Recent  Literature  Relating  to  Pharmacy,  {Amju°nUe?i902arm' 
coffee  are  chemical  antidotes  against  alkaloids  and  metallic  poisons, 
he  states  that  this  belief  appears  to  be  based  solely  on  clinical 
experience  and  upon  the  fact  that  both  beverages  contain  some  form 
of  tannin,  gallotannic  acid  being  known  to  precipitate  both  of  the 
above  classes  of  poisons.  The  clinical  results  might  be  due  to  the 
physiological  effects  of  the  caffeine  rather  than  the  chemical  action 
of  the  tannin,  as  in  the  use  of  coffee  in  opium  poisoning.  That  the 
tannin  of  both  tea  and  coffee  should  be  gallotannic  acid  seems  improb- 
able in  the  absence  of  experimental  support  of  this  statement 
(which,  apparently,  has  not  been  reported),  since  the  different 
tannins  are  known  to  differ  widely  in  composition  and  reactions. 
Ordinary  tannin — gallotannic  acid — is  an  anhydride  of  digallic  acid. 
Tea-tannin  may  be  (Dragendorff,  Pftanz analyse,  1882,  s.  166) 
practically  identical  with  gallotannic  acid,  or  with  quercotannic  acid 
(Rocheleder  quoted  in  Beilstein,  1897,  Vol.  3,  p.  688),  or  be  an 
entirely  different  substance  (Stenhase,  American  Journal  of  Phar- 
macy, 1862,  p.  254). 
Coffee-tannin  is  radically  different  from  tea-tannin,  being  a  digly- 
cosyl  ether,  of  3-4  cinnamic  acid.  The  very  markedly  less  astrin- 
gency  of  coffee  as  compared  with  tea  would  indicate  that  the  tannins 
of  these  two  substances  were  not  identical,  especially  when  it  is 
noted  that  unroasted  coffee  contains,  according  to  Spencer  (G.  L. 
Spencer,  "  Tea,  Coffee  and  Cocoa  Preparations,"  U.  S.  Department  of 
Agriculture,  Bulletin  13,  1892),  from  5-8  to  33-8  per  cent,  of  tanninr 
while  tea  contains  only  from  4  8  to  15*4  per  cent.,  the  latter  being  a 
very  rare  figure.  Notwithstanding  this  smaller  content  in  tanninF 
tea  is  in  practice  usually  preferred  to  coffee  as  a  chemical  antidote.1 
In  order  to  determine  the  chemical  reaction  of  tea  and  coffee 
with  different  alkaloids  and  metals,  and  to  ascertain  how  far  the 
general  statement  of  text-books  that  tannin  precipitates  "  most  alka- 
loids and  metals"  is  true,  Dr.  Sollmann  carried  out  the  following 
experiments: 
1  May  there  not  be  a  larger  percentage  of  tannin  in  unroasted  coffee  than 
in  roasted  ?  In  other  words,  do  not  the  destructive  changes  that  take  place  in 
green  coffee  during  the  process  of  roasting  destroy  some  of  the  tannin  ?  As  is 
well  known,  isolated  tannin  is  markedly  affected  by  heat — swelling,  blacken- 
ing and  igniting,  according  to  temperature  (U.  S.  D.,  1899,  100) — and  green 
coffee  on  being  roasted  is  heated  to  a  temperature  that  is  destructive  of  some 
of  its  constituents,  including,  possibly,  some  of  its  tannin. — J.  W.  E. 
